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Biomedical subjects

R L Johnson

Publications and source records attributed to R L Johnson.

At least 307 records · Page 17Linked to original sources
PubMed1983

Inhibition of renin by angiotensinogen peptide fragments containing the hydroxy amino acid residue 5-amino-3-hydroxy-7-methyloctanoic acid.

The 3R,5S and 3S,5S diastereoisomers of the hydroxy amino acid 5-amino-3-hydroxy-7-methyloctanoic acid (AHMOA) were synthesized from L-leucine and then incorporated into various peptide fragments of angiotensinogen to give the following polypeptides: AHMOA-Val-Phe-OCH3, His-AHMOA-Val-Phe-OCH3, and AHMOA-Ile-His-OCH3. These compounds were tested in an in vitro renin assay system for their ability to inhibit either hog kidney renin or human amniotic renin. The most active analogue of the series was (3R,5S)-AHMOA-Val-Phe-OCH3 (16). Against hog kidney renin, this compound possessed a Ki = 1.7 X 10(-4) M, while against human amniotic fluid, 16 had a Ki = 0.95 X 10(-4) M. The analogues AHMOA-Val-Phe-OCH3 and His-AHMOA-Val-Phe-OCH3 exhibited noncompetitive kinetics when the 3R,5S isomer of AHMOA was employed and competitive kinetics when the 3S,5S diastereoisomer of AHMOA was used.

Amino Acid Sequence↗
PubMed1983

Pseudotumor of the pancreas.

A 29-year-old black woman had a peculiar variety of chronic pancreatitis that initially presented as a solid, discrete mass in the head of the pancreas. It mimicked carcinoma and exemplifies the diagnostic and therapeutic dilemma produced by such "pseudotumors" of the pancreas.

Adult↗
PubMed1983

Cardiac output measurement using N2O uptake: a method to subtract cardiogenic oscillations.

Plethysmographic (box) methods using N2O uptake to measure pulmonary capillary blood flow, right ventricular stroke volume, and pulmonary arterial flow pulse conduction time have been complicated by the presence of so-called "cardiogenic oscillations" in the box flow records on air and N2O breathing. The exact cause of these oscillations is unknown but believed to be secondary to instantaneous changes in net blood flow into and out of the thorax during the cardiac cycle. We examined these oscillations and pulmonary capillary blood flow in normal human subjects in a flow plethysmograph using a pressure compensation circuit to extend the frequency response. The cardiogenic oscillations in flow recorded at the mouth (with glottis open) are much greater in amplitude and 90 degrees out of phase from those recorded from the plethysmograph. We derived a theoretical analysis of this and designed an analogue electrical circuit to enable us to eliminate these oscillations by electrical subtraction from the box flow record generated by N2O uptake in the pulmonary capillary bed. Measurements of pulmonary capillary blood flow and ventricular stroke volume using our method correlate with measurements made with acetylene-rebreathing blood flow measurements performed sequentially at the same sitting.

Capillaries↗
PubMed1983

Phosphorus bioavailability in the chick: effects of protein source and calcium level.

Three experiments utilizing 1,104 broiler cockerels were conducted to establish optimum dietary conditions for the determination of phosphorus (P) bioavailability. The reference P source was KH2PO4. A response-surface design and purified diets containing casein as the protein source were utilized in Exp. 1 Various levels of calcium (Ca) and P supported near-maximal gain in tibia ash. Optimal gain in tibia ash was attained at 1.8% Ca and .55% total (highly available) P. Regression equations describing the gain in tibia ash in response to added P from KH2PO4 for diets in Exp. 2 that contained casein and isolated soybean protein had different (P less than .05) slopes. Diets moderately limiting in available P exhibited reduced gain in tibia ash content if more than 1.4% total Ca was present. A corn-soybean meal diet was utilized in Exp. 3. Partitioning of tibia ash gain into effects due to basal diet, added P from KH2PO4, or P from the test ingredient was investigated. Sunflower meals containing 42 or 28% crude protein were evaluated for P bioavailability. The P content of the meals was 21.6 and 22.7% available, respectively. The fiber of the sunflower hull did not interfere with P availability. Selection of diet ingredients is discussed with respect to the development of P bioavailability values for use in practical diets.

Animals↗
PubMed1983

Measurement of human converting enzyme level by direct radioimmunoassay.

CE was purified from human lung, and antisera were raised in rabbits. Antisera inhibited the activity of the purified enzyme from lung and kidney and the plasma CE of normal persons and sarcoid patients. With antisera at a titer of 1:100,000, a sensitive, direct RIA was developed. CE purified from lung or kidney and CE present in normal and in sarcoid plasma gave parallel logit-log displacement lines, suggesting immunological identity. The level of CE in normal human plasma was 400 +/- 131 ng/ml. In untreated sarcoid patients, the enzyme level and activity increased in parallel. There was a negative correlation (r = -0.81) between enzyme level and diffusing capacity of the lung for CO in sarcoid patients. Synthetic inhibitors such as captopril or MK 421 did not interfere with the RIA, permitting enzyme levels to be monitored in patients undergoing acute inhibitor therapy. During administration of MK 421, CE activity was negligible and plasma levels of CE did not change. In contrast, renin activity increased eightfold during the inhibitor therapy.

Adult↗
PubMed1983

The diagnostic accuracy of exercise electrocardiography--a review.

The cardiovascular "stress test," and particularly the graded treadmill exercise test, has gained wide acceptance as a diagnostic aid in searching for ischemic heart disease and as a prognostic indicator for those with known coronary artery disease. Controversies still exist, however, in its use in mass screening and in interpreting equivocal tests. A review of the use and value of electrocardiographic exercise testing is presented. Topics such as its use in asymptomatic individuals, the adjuvant use of clinical examination, and the examination of ancillary treadmill parameters are presented. No attempt is made to detail the very significant contributions of radionuclide scanning. The positive exercise electrocardiogram in the asymptomatic subject is discussed and guidelines for clinical management are offered.

Angiocardiography↗
PubMed1983

Nutrient Analysis System--a computerized seven-day food record system.

A self-recording, directly computer-readable, seven-day food record system (the Nutrient Analysis System [NAS]) was developed using the National Heart, Lung, and Blood Institute Food Table as a data bank for the nutrient analysis. This article describes the system and reports the results of a study which evaluates the system in an experimental setting. It is concluded that the Nutrient Analysis System is no less accurate or biased than the traditional written food record method under the conditions of this test. Additionally, NAS is a system which allows for efficient use of professional time and immediate availability of nutrient analysis for use in counseling.

Adult↗
PubMed1983

Cellular immunity in ankylosing spondylitis. Lack of response to spinal tissue antigens.

In the studies reported here, peripheral blood lymphoid cells from 14 ankylosing spondylitis (AS) patients and 14 normal control subjects were examined for immune responses to the mitogens concanavalin A, phytohemagglutinin-P and pokeweed mitogen, as well as to primate spinal ligament, disc, and sacroiliac cartilage whole antigens. AS lymphocytes responded normally to mitogens and did not proliferate on exposure to spinal antigens. Assay for released supernatant proliferation inhibitory factor, tested on human HeLa cells monolayers failed to detect lymphokine release by AS lymphoid cells during exposure to spinal antigens.

Adult↗